Ultrasonic inspection of articles

Abstract

A method of ultrasonically inspecting an article comprises the following steps: transmitting a succession of ultrasonic pulses into the article; for each transmitted pulse, detecting and registering electrically the reflected pulse from the front surface of the article; detecting and registering electrically, with a predetermined gain, any reflected pulses indicative of faults or discontinuities within the article; detecting and registering electrically, again with a predetermined gain, at least the first reflected pulse from the rear surface of the article; monitoring the amplitudes of the registered reflected pulse from the front surface and at least the first reflected pulse from the rear surface of the article; and continuously controlling gains for succeeding pulses in dependence on the amplitude of the reflected pulse from the front surface of the article.

We claim 
     
       1. A method of ultrasonically inspecting an article comprising transmitting a succession of ultrasonic pulses into the article; for each transmitted pulse, detecting and registering electrically the reflected pulse from the front surface of the article; detecting and registering electrically, with a predetermined gain, any reflected pulses indicative of faults or discontinuities within the article; detecting and registering electrically, again with a predetermined gain, at least the first reflected pulse from the rear surface of the article; monitoring the amplitudes of the registered reflected pulse from the front surface and at least the first reflected pulse from the rear surface of the article; and continuously controlling gains for succeeding pulses in dependence on the amplitude of the reflected pulse from the front surface of the article. 
     
     
       2. A method of ultrasonically inspecting an article comprising transmitting a succession of ultrasonic pulses into the article; for each transmitted pulse, detecting and registering electrically the reflected pulse from the front surface of the article; detecting and registering electrically, with a predetermined gain, any reflected pulses indicative of faults or discontinuities within the article; detecting and registering electrically, again with a predetermined gain, at least the first reflected pulse from the rear surface of the article; monitoring the amplitudes of the registered reflected pulse from the front surface and at least the first reflected pulse from the rear surface of the article; continuously controlling gains for succeeding pulses in dependence on the amplitude of the reflected pulse from the front surface of the article; and maintaining the amplitude of the detected and registered reflected pulse from the front surface of the article at a predetermined level by means of an automatic gain control system. 
     
     
       3. A method as claimed in claim 2 wherein the automatic gain control system is applied to the reflected pulse from the front surface of the article and to subsequent fault and rear surface reflected pulses. 
     
     
       4. A method as claimed in claim 2 wherein the said gains include at least one step gain superimposed on the automatic gain and applied to reflected pulses after the reflected pulse from the front surface of the article. 
     
     
       5. A method as claimed in claim 4 wherein the step gain is such as to raise, with a defect free article, the amplitude of the first reflected pulse from the rear surface to the amplitude of the reflected pulse from the front surface of the article. 
     
     
       6. A method as claimed in claim 5 wherein the amplitude controlling gains for succeeding pulses is taken either from the front surface of the article or from the first reflected pulse from the rear surface of the article. 
     
     
       7. A method as claimed in claim 2 wherein the first and second reflected pulses from the rear surface of the article are detected and registered electrically with predetermined gains. 
     
     
       8. A method as claimed in claim 7 wherein a first step gain is applied to reflected pulses after the reflected pulse from the front surface of the article and a second step gain is applied to reflected pulses after the first reflected pulse from the rear surface. 
     
     
       9. A method as claimed in claim 8 wherein the first and second step gains are such as to raise, with a defect free article, the amplitudes of the first and second reflected pulses from the rear surface of the article to the amplitude of the reflected pulse from the front surface of the article. 
     
     
       10. A method as claimed in claim 8 wherein a time increasing ramp gain is applied after each step gain. 
     
     
       11. A method as claimed in claim 2 wherein the gains are continuously adjustable. 
     
     
       12. Apparatus for ultrasonically inspecting an article comprising means for transmitting a succession of ultrasonic pulses into the article; means for each transmitted pulse, for detecting and registering electrically the reflected pulse from the front surface of the article; means for detecting and registering electrically, with a predetermined gain, any reflected pulses indicative of faults or discontinuities within the article; means for detecting and registering electrically, again with a predetermined gain, at least the first reflected pulse from the rear surface of the article; means for monitoring the amplitudes of the registered reflected pulse from the front surface and at least the first reflected pulse from the rear surface of the article; means for continuously controlling gains for succeeding pulses in dependence on the amplitude of the reflected pulse from the front surface of the article; and an automatic gain control system for maintaining the amplitude of the detected and registered reflected pulse from the front surface of the article at a predetermined level. 
     
     
       13. Apparatus as claimed in claim 12 wherein the automatic gain control system is applied to the reflected pulse from the front surface of the article and to subsequent fault and rear surface reflected pulses. 
     
     
       14. Apparatus as claimed in claim 12 including means for detecting and registering electrically the first and second reflected pulses from the rear surface of the article with predetermined gains. 
     
     
       15. Apparatus as claimed in claim 14 including means for applying a first step gain to reflected pulses after the reflected pulse from the front surface of the article and means for applying a second step gain to reflected pulses after the first reflected pulse from the rear surface. 
     
     
       16. Apparatus as claimed in claim 15 including means for applying a time increasing ramp gain after each step gain.